1. Field of the Invention
Embodiments of the present invention generally relate to methods and apparatus for cleaning showerheads, such as those used for metal organic chemical vapor deposition (MOCVD) and/or hydride vapor phase epitaxy (HVPE).
2. Description of the Related Art
Chemical vapor deposition (CVD) chambers are typically utilized in the manufacture of semiconductor devices. A gas distribution showerhead is typically utilized to deliver precursors to a processing zone above a substrate located in the chamber, to deposit materials, such as thin films, onto the substrate. The gas distribution showerhead, as well as other hardware components in proximity of the processing zone in these chambers, such as the chamber body, is generally fabricated from low emissivity materials, such as aluminum. The aluminum surfaces are typically anodized to resist oxidation and/or corrosion. However, aluminum components may not be suitable for high temperature CVD processes, such as processes requiring temperatures in excess of 500 degrees C. to about 1400 degrees C. due, at least in part, to thermal expansion and contraction of aluminum materials. Further, the elevated processing temperatures may exceed the melting point of aluminum.
Other materials for use in high temperature CVD processes have been investigated. One of these materials is ceramic, which is corrosion resistant, has a low reflectance and is capable of withstanding elevated processing temperatures without deformation. However, some processes, such as chamber cleaning processes, require plasma formation facilitated by an electrical bias between the gas distribution showerhead and other components in the chamber. The dielectric properties of ceramic materials are not suitable to deliver electrical signals to facilitate plasma formation in these processes.
Another of theses materials is stainless steel, which is relatively corrosion free, has a high reflectance and low emissivity, and it suffers a slow rate of oxidation as compared to other metals such as aluminum. Stainless steel is conductive and may be effectively utilized to facilitate plasma formation. However, stainless steel has a low emissivity, is subject to oxidation, and must be cleaned or de-oxidized periodically.
In high temperature CVD processes, temperatures in the processing zone are desired to be stable to provide repeatable wafer-to-wafer and within-wafer deposition results. One factor affecting the temperature in the processing zone is the emissivity of the chamber hardware. When the chamber hardware is in a new condition, i.e., non-oxidized or corroded by process gas chemistries, the emissivity is known and is typically low. However, during processing, the emissivity of these materials may change due to adhesion of precursor materials on the exposed surfaces, or corrosion or oxidation of these exposed surfaces. The emissivity change affects thermal parameters in the processing zone, which causes process drift. Before the condition of the process components affects the process condition adversely, the chamber components must be cleaned or replaced.
The hardware components are typically cleaned on a schedule, such as after they are exposed to process conditions for a certain number of hours determined experimentally such that at the end of the period, the process yields acceptable deposition results on the substrate despite the process drift. The cleaning of the components is intended to restore the component to its original condition, and thus restore the process chamber to a condition where it would perform as though new, clean components were installed therein. However, it has been found, in particular with respect to non-ceramic chamber components, that the components when cleaned do not result in the chamber performing at the same condition as it had when the components were new. Then, in use, the cleaned components likewise exhibit emissivity changes, in the same manner as new components. Because the chamber properties are different, as compared to new components, when the cleaned components are first installed, using the cleaned components for the same process period as new components results in process conditions which may yield unacceptable deposition results on substrates.
Therefore, there is a need for a gas distribution showerhead, and other components in proximity of the processing zone in these chambers, that reduces process drift and enables a closer emissivity match between new and cleaned components. Additionally, there is a need for a method of cleaning to produce a repeatable surface.